CH717234A1 - Process for the production of a PET starting material suitable for use in an extrusion blow molding process and hollow bodies produced therefrom. - Google Patents

Abstract

The subject matter of the invention is a process which consists of a “Bottie Grade PET post-consumer recycling flake” of a polyester starting material suitable for use in an extrusion blow molding process, ie a recycled post-consumer PET with a viscosity of 0.65 to 0.84 dl / g EBM makes bottle with 0.90 to 1.5 dl / g with the help of extrusion processes, solid state polycondensation processes and a blowing process.

Description

Field of invention

The present invention relates to a method for producing a polyester starting material suitable for use in an extrusion blow molding process for producing a hollow body made of plastic, in particular a plastic bottle, according to the preamble of claim 1, and a hollow body produced by extrusion blow molding according to the preamble of claim 29 .

State of the art

For the production of PET containers on extrusion blow molding machines, the extrusion blow molding can only be used if the PET molding compound has the necessary melt strength, that is, the plastic tube when closing the blow mold halves has a shape and consistency that increases during the subsequent inflation and curing lead a hollow body that meets the specified specifications. This applies in particular to Shuttle extrusion blow molding machines, where the tube is exposed to gravitational forces for a very long time. The melt strength of the PET material, which is used for the stretch blow molding process, in which the containers are formed from a preform produced in an injection molding process, does not meet the requirements for extrusion blow molding, since its intrinsic viscosity is too low and at Use in extrusion blow molding leads to said inadmissible lengths of the plastic tubing. The PET material must be modified accordingly for extrusion blow molding.

According to the prior art, PET molding compounds are used for extrusion blow molding, which are known under abbreviations such as PET X (extrudable), PET G (glycol modified) and PET B (branched). Terms such as EPET or E-PET (especially in the USA) or EBM PET are also used. These are PET materials specially developed for extrusion blow molding, the quantity of which is produced is low and therefore has a correspondingly high price. The PET hollow bodies produced with these PET molding compounds can be easily fed into the recycling stream. However, these hollow bodies cannot be blown with the standard recycling material on the market, as this standard recycling material has the usual viscosity of the most common bottled goods, but EBM requires a higher viscosity.

Standard PET types are linear PET types (not branched) with a low copolymer content of less than 5% by weight and an intrinsic viscosity (IV) between 0.72 and 0.86 dl / g (according to ASTM D 4603).

The PET, which is mainly used today for the production of bottles in a stretch blow molding process, is a PET with an intrinsic viscosity (IV) between 0.72 and 0.86 dl / g measured according to ASTM D4603. When processing the PET with the one or two-stage stretch blow molding process (in English: Injection Stretch Blow Molding = ISBM), which is most commonly used in practice, the material typically reduces viscosity between 0.01 and 0.09 dl / g.

In the PET recycling process used nowadays, the reduction in viscosity that occurred in the manufacturing process is compensated for again with the aid of solid phase polycondensation (hereinafter also referred to as "SSP process"; 72 to 0.86 dl / g reached.

In contrast to the stretch blow molding process most frequently used for the production of PET bottles, however, extrusion blow molding (EBM) requires viscosities between 0.9 and 1.4 dl / g. This means that the material produced in the standard PET recycling process and also the usual regenerates cannot be used for the EBM process

According to more recent legislation, however, the plastics industry is obliged to use up to 35% recycled material in newly manufactured bottles. This legal requirement applies to both the ISBM procedure and the EBM procedure. In principle, it would be desirable if the PET bottles produced in the EBM process, the material of which has an increased viscosity, could be collected separately so that they could be used again in an EBM process. Unfortunately, this is currently not possible for economic reasons, as the "economy of scale" does not allow this separate collection and recycling electricity for very small quantities.

In the standard PET recycling stream, however, the highly viscous EBM bottles, which usually only occur in small quantities, do not interfere, since the "cross esterification" occurring in the melt mutually align the chains.

However, the viscosity of the standard PET recycling stream is much too low to 20 percent by weight. or to be able to add more recycled PET material to an EBM process.

EP2747981B1 and EP2807082B1 describe that PET for ISBM (typical virgin material has an intrinsic viscosity IV between 0.72 and 0.86dl / g) for use in an EBM process via solid phase polycondensation to an IV of 0.96 to 1.4dl / g can be brought.

WO2018127431 (A1) discloses a method to raise material from the standard PET recycling stream to the desired viscosity by means of a longer residence time in the SSP reactor. However, a longer residence time in the SSP reactor also has decisive disadvantages: The longer residence time, for example, throttles the output of the recycling plant by 2 to 8 times, depending on the target viscosity. In addition, the longer residence time in the SSP reactor leads to more yellowing of the material.

An alternative way to increase the molecular mass of PET is the use of so-called chain extenders. The chain extension of rPET by using the chain extender pyromellitic dianhydride (PMDA) by means of reactive extrusion is known in the prior art. Reactive extrusion means that the rPET in the melt reacts directly with the PMDA during the dwell time in the extruder and is immediately used in a forming or primary forming process.

EP0748346B1 discloses a method for increasing the molecular weight of polyesters, in which a mixture of a polyester and a tetracarboxylic acid dianhydride and a sterically hindered hydroxyphenylalkylphosphonic acid ester, for example Irganox <®> 1425 (BASF), in the case of crystalline polyesters above the melting point or in the case is heated by amorphous polyesters above the glass transition temperature.

EP1054031B1 describes a somewhat different formulation compared to EP0748346B1 for chain extension of polyesters (also rPET), where in addition to a polyfunctional anhydride (polyanhydride) (= component a), at least one polyfunctional compound whose functional groups can react with the anhydride groups of the polyanhydride ( = Component b), at least one phosphonate (= component c) is used. A polyol, a polyfunctional epoxy compound, a polyamine, polyaziridine, polyisocyanate, polyoxazoline or a polyfunctional thioalcohol can be used as component b. In the reactive extrusion of the aforementioned 3-component mixture together with a polycondensation polymer, the molecular weight can be greatly increased in short reaction times. It was found that the addition of polyfunctional components does not result in crosslinked polycondensates, but rather that the polyfunctional compounds are essentially built into the chain and lead to chain extensions and / or branches. For reactive extrusion, temperatures are proposed which are preferably in the range between the melting temperature and a temperature about 50 ° C. above the melting temperature. In the case of amorphous polyesters, the reaction takes place in the range between 50 ° C and 150 ° C above the respective glass transition temperature.

It should also be possible to produce extrusion blow-molded products from the modified polycondensate. A disadvantage of this approach is that the higher the number of chain extenders used, with or without chain branches, the greater the risk of crosslinking and gel formation (see Awaja et al (2004)). These gels are visible as specks (= highly viscous grains) in extrusion blow molded hollow bodies and represent an optical defect. In addition, cross-linked polyesters may tend to be hindered in their crystallization, which can lead to considerable problems if the material does not pass through the PET recycling stream again crystallized. Typically, the tool of choice for reactive extrusion is the twin-screw extruder (Awaja and Pavel (2005)).

Typical EBM PET types that are used today for the production of bottles in an EBM process are, for example, Indorama Polyclear 5507, PETKO PET 160-X. Typical EBM PET types usually have the narrow molecular weight distribution typical of polycondensates without significant long chain branching and thus result in a low melt elasticity. This manifests itself in low elastic restoring forces when exiting the nozzle gap, which results in a slight swelling of the diameter and thickness of the hose. This has the disadvantage that the free-hanging hose in extrusion blow molding changes much more quickly than the materials normally used in extrusion blow molding, such as HDPE or PP, and therefore has a significantly narrower process window.

Task

The object of the present invention is to provide a material for extrusion blow molding, in particular of PET bottles, which preferably comes primarily from rPET, which is obtained from the collection of post-consumer PET articles, in particular from PET bottles will. In particular, it is an aim that the material be compatible with the PET recycling stream and be partially crystalline. Another aim is for the material to have a high melt stiffness and therefore be particularly suitable for extrusion blow molding. Another goal is that as few additives as possible are added for the production of the material in order not to significantly impair the purity of the PET recycling stream. Another goal is that the production of the material is significantly faster than the pure condensation of rPET in a solid-phase polycondensation. In addition, the material should be low-gel and deliver bottles with few specks when used.

Definitions:

In the context of the present invention, the term “viscosity” is understood to mean the intrinsic viscosity (IV) measured according to the ASTM 4603-03 standard.

In the context of the present invention, “pure PET” is understood to mean that PET has been sorted within the framework of today's technological possibilities, so that the weight percentage of non-varietal plastic is less than 2%, preferably less than 1% and particularly preferably less than 0.5 % is.

In the present case, rPET is used as an abbreviation for recycled post-consumer PET.

"Bottle Grade PET Post-consumer Recycling Flake" is rPET which has been processed into flakes and which comes from the collection of post-consumer PET articles, in particular from PET bottles

In the context of the present invention, EBM-PET is understood to mean PET (including PET copolymers) which is suitable for use in an EBM process, i.e. has an IV between 0.87 dl / g and 1.4 dl / g.

description

According to the invention, the object is achieved in a method according to the preamble of claim 1 in that the intrinsic viscosity of the extruded granulate is further increased by a subsequent heat treatment in a solid phase post-condensation (solid state polycondensation, SSP). Surprisingly, the viscosity can again be increased significantly by means of a solid-phase post-condensation. This effect was unexpected because it had to be assumed that the chain extender or chain branch added in process step d) has already reacted and no further chain lengthening takes place. In addition, the granulate in the SSP reactor is not in the form of a melt, but in a partially crystalline state. Compared to the melt, the chain mobility is reduced in the amorphous zones and even greatly reduced in the crystallites, which should lead to a greatly reduced reactivity, especially in the crystalline areas. Overall, the chain mobility is already lower, since the SSP operates below the melting temperature and significantly above it in reactive extrusion. The Arrhenius approach for reaction rates shows that an increase in temperature by 10K results in approximately a doubling of the reaction rate. Accordingly, the person skilled in the art could not expect that, given the restricted mobility of the molecules, a further, substantial condensation could take place.

The solid-phase post-condensation is preferably carried out at temperatures 225 ° C. This has the advantage that the granulate is spared and yellowed less than at even higher temperatures, which in an SSP process for PET is typically 225 ° C. or higher (cf. EP 1 054 031, [108]).

The increase in viscosity in process step f) is preferably higher than that in process step d). This increase in viscosity in process step f) is surprising to the person skilled in the art, since the PET in process step f) is not present as a melt, but rather as granules.

In a further embodiment of the invention, the residence time of the granules in the SSP reactor is less than 20 hours, preferably less than 15 hours and particularly preferably less than 12 hours.

The relatively short residence time can not only shorten the manufacturing process, but also prevents yellowing of the granules, which occurs if the residence times are too long.

In a further embodiment of the invention, the post-consumer PET material used in method step a) has a viscosity between 0.65 and 0.84 dl / g. The starting material therefore has a low viscosity and can nevertheless be converted by the inventive method into a material with a corresponding viscosity that can be used for an EBM process.

The method advantageously enables the viscosity of the material used to be increased by 0.05 to 0.2 dl / g through the reactive extrusion.

According to a further embodiment of the invention, the viscosity is increased by a further 0.1 to 0.6 dl / g, preferably by 0.15 to 0.55 dl / g and particularly preferably by 0.3 to 0 with the aid of the solid phase post-condensation .55 dl / g increased. The viscosity of the PET starting material can therefore be increased in an SSP reactor and in a reactive extrusion.

It is advantageous if the temperature during extrusion and the amount of chain extender is chosen so that the extruded material has an intrinsic viscosity (IV) greater than 0.75 dl / g, in particular between 0.75 and 0.9 dl / g preferably between 0.8 and 0.9 dl / g. This viscosity is ideally suited for the production of a hollow body made of plastic in the EBM.

A polyfunctional anhydride, i.e. a molecule with two or more anhydride groups, is advantageously used as the chain extender.

According to a further embodiment of the invention, tetracarboxylic acid dianhydrides are used as chain extenders.

According to a further embodiment of the invention, pyromellitic dianhydride is used as the chain extender.

According to a further embodiment of the invention, one of the following chain extenders is used: bisoxazolines, bisepoxides, diisocyanates, polyepoxides, compounds containing several glycidyl groups, maleic anhydride, phthalic anhydride, triphenyl phosphates, lactamyl phosphites, cyclo-phosphazene, polyacyllactam, and Bis-2-oxazolines, bis-5,6-dihydro-4h-1,3-oxazines, diisocyanates, trimethyl 1,2,4-benzenetricarboxylate (trimethyl trimellitate, TMT), carbonyl bis (1-caprolactam). These are typical chain extenders and have proven themselves for reliable chain extension with rPET.

Polyols and polycarboxylic acids are advantageously used as chain branches.

Compounds with more than two hydroxyl groups are advantageously used as chain branches.

Glycerol, pentaerythritol or a combination of both compounds are advantageously used as polyols.

According to a further embodiment of the invention, between 0.05% by weight and 1.0% by weight of chain extender is added to the rPET.

According to a further embodiment of the invention, the extruded melt is filtered before granulation. A further chain build-up preferably takes place after the filter in order to avoid excessively high melt pressure.

According to a further embodiment of the invention, the extruded melt is pressed through a perforated filter with a hole size between 30 μm and 300 μm and preferably between approximately 50 μm and 100 μm. As a result, the melt has sufficient purity and cloudiness and impurities can be prevented in the end product of a hollow body.

According to a further embodiment of the invention, an acid scavenger is added to the PET material prior to extrusion. Acid scavengers prevent the acid-catalyzed chain cleavage (hydrolysis) of PET in the melt.

According to a further embodiment of the invention, calcium stearate, zinc stearate, zinc oxide or hydrotalcite or a combination of the aforementioned acid scavengers is used as the acid scavenger.

According to a further embodiment of the invention, the material is degassed during extrusion. The degassing allows the viscosity of the material to be increased by a further 0.01 to 0.1 dl / g.

According to a further embodiment of the invention, the rPET material obtained in method step f) is fed to the EBM system, and a chain extender is added to the EBM system. This increases the viscosity through reactive extrusion. The fine adjustment of the required viscosity can therefore be carried out on the blow molding machine. For example, the extruded tube for the production of smaller bottles requires a lower viscosity, since lower tensile forces arise from the force of gravity.

According to a further embodiment of the invention, the melt is divided into thin layers or strands in the extruder. This massively increases the surface of the material.

According to a further embodiment of the invention, the extrusion takes place in a vacuum or in a protective gas atmosphere, in particular under nitrogen. This increases the viscosity by 0.1 to 0.5 dl / g. This form of extrusion is particularly efficient when the surface of the melt is enlarged by dividing it into layers and strands.

According to a further embodiment of the invention, a tube or a plurality of tubes is extruded, blown into one or more hollow bodies and then cut off. According to a further embodiment of the invention, a tube or a plurality of tubes is extruded, cut off and then blown into one or more hollow bodies.

The strength of the hose is advantageously increased by 5 to 50 ° C. through active cooling.

The hose is advantageously cooled by expanding the hose, coming into contact with another medium, by blowing nozzles, aerosols or other forms of heat dissipation, in particular by means of heat pipes.

According to a further embodiment of the invention, the PET “untreated” PET (virgin material or rPET) with an IV (intrinsic viscosity) of 0.6 to 0.95 dl / g in a mass fraction of 0 to 50% is added to the Melt strength can be adjusted for each item. The high melt strength of the treated PET allows the addition of untreated PET. This makes it possible to reduce the price of the starting material for producing a hollow body.

Another aspect of the invention relates to a hollow body, in particular a bottle, made of at least partially recycled PET. The hollow body is characterized in that the PET starting material for producing the hollow body is between 30% by weight. and 100% by weight. Contains rPET with an intrinsic viscosity between 0.90 and 1.5 dl / g and an extensional viscosity of more than 6500 Pa * s (275 ° C, 50s, as well as between 70 wt.% and 0 wt.% vPET.

The hollow body can advantageously be obtained from a method as described above.

According to a further embodiment of the invention, the recycled PET is produced from recycled post-consumer PET (“bottle grade PET post-consumer recycling flake”) with a viscosity between 0.65 and 0.84 dl / g by condensation.

The PET starting material of the finished hollow body advantageously has a shear viscosity at 275 ° C. and 50 s <-1> of less than 3000 Pa * s, in particular between 1000 and 2500 Pa * s. According to a further embodiment of the invention, the PET starting material for producing the hollow body has an extensional viscosity (at 275 ° C, 50s-1) of at least 5500 Pa * s at 275 ° C when producing hollow bodies with a volume between 100 ml and approximately 500 ml and more than 7000 Pa * s for hollow bodies with a volume of more than 500 ml and preferably more than 600 ml, and in particular between 7000 Pa * s and 14000 Pa * s.

Exemplary tetracarboxylic dianhydrides which can be used as chain extenders are pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, 1,1,2,2-ethanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 5-diphenylsulfonetetrahydride, 5-diphenylsulfonetetracarboxylic acid -3-furanyl) -3-methyl-3 cyclohexane-1,2-dicarboxylic acid dianhydride, bis (S, 4-dicarboxylic acid phenyl) ether dianhydride, bis (3,4-dicarboxylic acid phenyl) thioether dianhydride,, 2,2-bis- (3,4-dicarboxylic acid phenyl) -hexafluoropropane dianhydride, 2,3,6,7-naphthalene-tetracarboxylic acid dianhydride, bis- (3,4-dicarboxylic acid phenyl) -sulfonic dianhydride, 1,2, 5,6-naphthalene-tetracarboxylic acid dianhydride, 2,2 ', 3,3'-biphenyltetracarboxylic acid dianhydride, hydroquinone bisether dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 1,2,3, 4-cyclobutanetetracarboxylic acid dianhydride, 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid dianhydride, bicyclo (2,2) oct-7-ene-2,3,5,6- tetracarboxylic acid dianhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic acid dianhydride, 4,4 '-Oxydiphthalic acid dianhydride (ODPA), ethylenediamine tetracarboxylic acid dianhydride (DDTAh), or combinations of these dianhydrides.

Examples:

Methods:

The melt rheological characterization was carried out in accordance with ISO 11443: 2014. Samples are dried in vacuo at 120 ° C. for 12 hours. A Göttfert Rheograph 75 with a 2x15mm test channel was used for testing. The 10/1 and 0 / 1mm capillaries were used. The test temperature was 275 ° C. A Bagley correction and a Rabinowitsch-Weissenberg correction were carried out. Both the shear and the extensional viscosity were determined. The extensional viscosity was determined using the Cogswell method (first description by Cogswell 1972) from the inlet pressure losses by means of WinRheo II software (Göttfert material testing machines GmbH, Buchen, Germany).

Example 1:

A commercially available virgin PET product for injection molding (IV 0.8 dl / g) was left in an SSP reactor at 215 ° C. for a period of 17 hours. When tested on an EBM system, the material exhibited relatively poor melt stiffness. A cosmetic bottle with a height of approx. 20 cm and a volume of approx. 400 ml was difficult to shape.

Examples 2-4:

Commercially available new EBM PET types were procured. A cosmetic bottle with a height of approx. 20 cm and a volume of approx. 400 ml could only be formed with difficulty from the material from Example 2. In contrast, the material from Example 3 was well suited for this. The material from Example 4 made it possible to form handle bottles with volumes of 1L or larger.

Example 5:

A commercially available rPET granulate consisting of “post-consumer” waste was procured and left in the SSP reactor at 210 ° C. for 15 hours. The material is suitable for the production of the cosmetic bottle described above.

Example 6:

A commercially available rPET granulate consisting of “post-consumer” waste was procured and left in the SSP reactor at 215 ° C. for 22 hours. The material is suitable for the production of the cosmetic bottle described above.

Examples 7 and 8:

[0063] Regrind from “post-consumer” PET waste (IV 0.792dl / g), for example in the form of flakes or snippets, was mixed with 0.105% PMDA in an extruder (Example 7: PMDA in a solid carrier; Example 8: PMDA in liquid carrier) and granulation. The IV of the resulting partially crystalline granulate was 0.847 dl / g (Example 7) or 0.867 dl / g (Example 8). The granules with a crystallinity between 40 and 60% were left in the SSP reactor at 200 ° C. for 10 hours. To the surprise of the inventors, the treated granules had a very high extensional viscosity, which was also reflected in the fact that these materials showed a very high or high tube stability on the EBM system. At the same time, due to the low shear viscosity in relation to the extensional viscosity, a low melt pressure has occurred in these materials.

Table 1: Material examples (measurement methods for shear and elongation viscosity see above)

1 PET new product, condensed - 215 ° C, 17h 1.193 1669 5331 Bad 2 EBM PET new product - 1.161 1891 5151 Bad 3 EBM PET new product - 1.292 2186 5677 Moderately 4 EBM PET new product - 1.400 3274 9088 Good 5 rPET, condensed - 210 ° C, 15h 1.198 2294 6826 Good 6 rPET, condensed - 215 ° C, 22h 1.239 1899 6610 Good 7 rPET mixed with PMDA and condensed 0.105% PMDA, solid carrier 200 ° C, 10h 1.194 1657 13192 Very good 8 rPET with PMDA added and condensed 0.105% PMDA, liquid carrier 200 ° C, 10h 1.074 1452 7641 good <a)> Using the Carreau approximation, the values for 50 s <-1> were derived from the measurement data, since the shear rates cannot typically be determined with such accuracy. The measuring range was typically in the range 10 to 3000 s <-1>. The determination was carried out as described under "Methods". <b)> Method according to Cogswell, determination by means of Göttfert WinRheo II software (Göttfert MaterialPrüfmaschinen GmbH, Buchen, Germany). Attention: measuring points interpolated from measuring data. The determination was carried out as described under "Methods".

Examples 7 and 8 show that by using the PMDA under “milder” reaction conditions (lower process temperature, significantly shorter residence time) it is possible to work in the SSP and even higher extensional viscosities can be achieved than without using the PMDA for the significantly longer ones Residence times and process temperatures in Examples 5 and 6. The comparison of Examples 1 and 5 or 6 shows that rPET can in principle have faster reaction kinetics than vPET (virgin material). However, the behavior of rPET can also fluctuate, depending on the composition of the incoming goods flow.

The examples also show that the intrinsic viscosity is generally not a suitable measure for the suitability of PET types for EBM. For example, examples 1 and 7 show an almost identical IV of 1.193 dl / g, respectively. 1.194 dl / g. The same applies to the shear viscosities with 1669 Pa * s and 1657 Pa * s at 275 ° C and 50s <-1>. At the same time, however, the two materials show massive differences in the extensional viscosity of 5331 Pa * s and 13192 Pa * s at 275 ° C and 50 s <-1>. One of the weaknesses of the IV is actually that relatively small amounts of sample are used for the determination in relation to melt rheological methods. In the case of materials with a tendency to inhomogeneities (which can certainly be recycled materials), this can result in strongly scattering IV measured values or generally. lead to a poor accuracy of the determination.

What is new and absolutely unexpected is the high swelling (diameter swelling) compared to all previously processed EBM PET types (new PET material as well as rPET-based). This is an indication of a high melt elasticity. This is atypical for PET, because PET typically has a narrow molar mass distribution due to production or cross-esterification and the polymer chains can therefore relax very quickly and PET melt typically has a low melt elasticity as a result. The following can typically be expected for PET: low melt stiffness Little or no tendency to swell at the nozzle outlet no or hardly any strain hardening in the melt

In contrast to expectations, the rPET treated according to the invention showed an unusual behavior characterized by a high melt elasticity or extensional viscosity, as described with reference to the above examples, and a high tendency to swell. The high extensional viscosity in relation to the low shear viscosity is an indication of a rather elastic nature of the rPET treated according to the invention. As a result of the resulting high elastic restoring forces, these materials show, in contrast to the materials from Examples 1 to 5 (materials with more plastic behavior), a much lower tendency to adhere to metallic surfaces. Without these elastic restoring forces, the melting behavior towards metallic surfaces would be dominated by the wetting behavior (surface tension).

Description of figure 1:

FIG. 1 shows the subjective “EBM rating” plotted against the Cogswell (EtaCo) extensional viscosity at 275 ° C. and 50 s <-1>. The “EBM rating” is as follows: Materials that caused difficulties even in the production of small bottles, as in Examples 1 and 2 above, were rated 0 (unsuitable) or 1 (difficulties with small bottle formats). Materials that could be processed without problems for the above cosmetic bottle were rated 3. Materials that would be suitable for bottles with 1L net capacity or slightly larger (up to 5L) were rated 4. In order to be able to take into account the even higher observed, subjective melt strength on the EBM system compared to class 4, class 5 was also introduced. It can be seen from FIG. 1 that the extensional viscosity defines a limit curve which is similar to part of a parabola. It is not known whether this limit curve conforms to an asymptote, as no data are available for this. This is currently not relevant for the intended use of the materials. The limit curve, however, clearly shows that the PET must have an extensional viscosity of at least 5500 Pa * s at 275 ° C. and 50 s in order for it to be suitable for extrusion blow molding of small hollow bodies, ie those with a volume between 100 ml and 500 ml is suitable, whereas for larger hollow bodies, ie for hollow bodies with a volume greater than 500 ml, at least 6500 Pa * s are required.

Description of the procedure:

In a first process step, post-consumer PET bottles are sorted, washed, cut and contaminants such as metal, paper and other contaminants are removed.

In a second process step, the cut PET flakes are dried. During the drying process, conditions can already be created in which the PET builds up molecular weight. (e.g. Vacurema process from EREMA Engineering Recycling Maschinen und Anlagen Ges.m.b.H., Ansfelden, Austria).

In a third process step, a chain extender and / or a chain branch is added to the PET, and a reactive extrusion of the flakes is carried out, preferably under vacuum. Under these conditions, the PET is rapidly condensed during extrusion, i.e. the mean molecular weight of the rPET increases. Instead of performing the extrusion under vacuum, it can also take place in a protective gas atmosphere.

Optionally, the rPET with the addition of the chain extender, respectively. of the chain branch additionally 0.01 to 1.0 wt .-%, preferably 0.05 to 0.8 wt .-% of an acid scavenger such as calcium stearate, zinc stearate, zinc oxide or hydrotalcite or a combination of these acid scavengers are added and then the extrusion of the flakes be performed. The acid scavenger can prevent or at least reduce the acid-catalyzed chain cleavage (hydrolysis) of PET in the melt.

Optionally, stabilizing phosphorus compounds in the form of an acid (e.g. H3PO4) or an acid ester in the range of 0 to 50 ppm can be added to the rPET.

In a subsequent process step, the melt is filtered (optional) and granulated.

In a subsequent process step, the granulate is placed in an SSP reactor and raised to a viscosity of over 0.9 dl / g.

In a subsequent process step, the material can be dried on the extrusion blow molding machine, the viscosity being increased again at the appropriate temperature. Optionally, the material can be mixed again with a chain extender and raised to a viscosity that is useful for the EBM process. The chain extender can be added before or at the same time as the extrusion.

The material is preferably transferred directly from the SSP reactor to the EBM plant. If, on the other hand, the material is filled into big bags or storage containers after the SSP process, for example, because it cannot be further processed directly, then the residual moisture is preferably set to below 50ppm, preferably below 30ppm (typically preferably by drying immediately before processing on the EBM- System).

Small bottles require a lower viscosity than larger ones, since the tube is smaller and lower tensile forces are created by gravity. The fine adjustment of the viscosity can therefore be carried out on the blow molding machine in relation to the product.

In the extrusion blow molding process, so-called slugs are obtained which are separated from the final bottle and preferably fed back into the process by comminuting them to flakes, the ground PET, and subjecting them to post-condensation in the SSP reactor or dryer. This allows the regrind PET to build up viscosity again. This is important because the intrinsic viscosity typically decreases by 0.03 to 0.3 dl / g during extrusion. A chain extender can optionally be added to the regrind PET to increase condensation.

In an optional process step, "untreated" PET (virgin material (vPET) or rPET) with an IV of 0.6 to 0.95 dl / g in a mass fraction of 0 to 50% can be added to the rPET treated as described above, to adjust the melt strength for each item. Because a high melt strength of the treated rPET can be achieved with the method according to the invention, this allows the admixture of untreated rPET or of vPET. This can reduce the cost of the process.

In an optional process step, there is a degassing zone in the extruder (process step d) which builds up the PET by 0.01 to 0.10 dl / g during extrusion.

In an optional process step, the melt is divided into thin layers or strands in the extruder, which massively increases the surface area of the material and makes it more accessible to melt polymerization (condensation). As a result, the intrinsic viscosity can be built up by 0.10 to 0.50 in the melt. This process step preferably takes place under vacuum or a protective gas atmosphere, e.g. under nitrogen.

In a subsequent process step, a tube is extruded and blown into a hollow body and cut. The remaining slugs above and below the bottle are removed.

In an optional process step, the strength of the extruded tube can be increased by cooling the tube by 5 to 50 ° C. The cooling is carried out either by expanding the hose, by contact with another medium, by blowing nozzles, by aerosols or other forms of heat dissipation, in particular by means of heat pipes. Due to the evaporation of a medium, heat pipes lead to a very uniform cooling with temperature differences of less than 1 ° C.

In summary, the subject matter of the invention is a method which comprises an EBM bottle from a “bottle grade PET post-consumer recycling flake”, ie a recycled post-consumer PET, with a viscosity of 0.65 to 0.84 dl / g 0.90 to 1.5 dl / g with the help of extrusion processes, solid state polycondensation processes and a blowing process.

Sources:

Awaja F., Pavel D. (2005), Review Recycling of PET, European Polymer Journal 41, pp 1453-1477 Awaja et al. (2004), Recycled Poly (ethylene terephthalate) Chain Extension by Reactive Extrusion Process, Polymer Engineering and Science, 44 (8), pp. 1579-1587 Cogswell F.N. (1972), Converging flow of polymer melts in extrusion dies, Polym. Closely. Sci. 12, pp. 64-73

Claims (33)

1. A method for producing a polyester starting material suitable for use in an extrusion blow molding process, in particular PET starting material, for producing a hollow body made of plastic, in particular a plastic bottle, in which method a) post-consumer PET articles, in particular PET bottles, sorted by type be sorted, washed and shredded, b) Contaminations such as metal or paper are removed before, simultaneously with or after process step a), c) the shredded PET material is then dried, d) the shredded PET material is then melted, a chain extender or chain branch is added, and the melt of shredded PET material and chain extender or chain branch is reactively extruded, the addition of the chain extender, respectively. of the chain branch before or during the melting process, and e) granules are produced from the melt, the condensed PET material also being referred to below for short as “EBM-PET”, characterized in that in a subsequent process step f) the intrinsic viscosity of the granulate is increased further by a subsequent heat treatment in a solid-phase post-condensation. 2. The method according to claim 1, characterized in that the viscosity increase in method step f) is higher than that in method step d). 3. The method according to claim 1 or 2, characterized in that the solid-phase post-condensation takes place at temperatures ≤ 225 ° C. 4. The method according to any one of claims 1 to 3, characterized in that the residence time of the granules in the SSP reactor is less than 20 hours, preferably less than 15 hours and particularly preferably less than 12 hours. 5. The method according to any one of claims 1 to 4, characterized in that the post-consumer PET material used in process step a) has a viscosity between 0.65 and 0.84 dl / g. 6. The method according to any one of claims 1 to 5, characterized in that the reactive extrusion increases the viscosity of the material used by 0.05 to 0.2 dl / g. 7. The method according to any one of claims 1 to 6, characterized in that with the help of the solid phase post-condensation the viscosity by a further 0.1 to 0.6 dl / g, preferably by 0.15 to 0.55 dl / g and particularly preferably by 0, 3 to 0.5dl / g, is increased. 8. The method according to any one of claims 1 to 7, characterized in that the temperature during extrusion and the amount of chain extender or chain branch is chosen so that the extruded material has an IV greater than 0.75 dl / g and in particular between 0. 75 and 0.9 dl / g, preferably between 0.8 and 0.9 dl / g. 9. The method according to any one of claims 1 to 8, characterized in that a polyfunctional anhydride, i.e. a molecule with two or more anhydride groups, is used as the chain extender. 10. The method according to any one of claims 1 to 8, characterized in that tetracarboxylic acid dianhydrides are used as chain extenders. 11. The method according to any one of claims 1 to 8, characterized in that pyromellitic dianhydride is used as the chain extender. 12. The method according to any one of claims 1 to 8, characterized in that one of the chain extenders mentioned below is used as the chain extender: bisoxazolines, bisepoxides, diisocyanates, polyepoxides, compounds carrying several glycidyl groups, maleic anhydride, phthalic anhydride, triphenyl phosphates, lactamyl phosphites, cyclo-phosphazene, polyacyllactam, and bis-2-oxazolines, bis-5,6-dihydro-4h-1,3-oxazines, diisocyanates, trimethyl 1,2,4-benzenetricarboxylate (trimethyl trimellitate, TMT), carbonyl bis (1-caprolactam) is used. 13. The method according to any one of claims 1 to 8, characterized in that polyols are used as chain branches. 14. The method according to any one of claims 1 to 8, characterized in that chain branch connections are used with more than two hydroxyl groups. 15. The method according to any one of claims 1 to 8, characterized in that the polyols used are glycerol, pentaerithritol or a combination of both compounds. 16. The method according to any one of claims 1 to 12, characterized in that between 0.05% by weight and 1.0% by weight, preferably between 0.1% by weight and 0.8% by weight and particularly preferably between 0.1% by weight and 0.6% by weight , to Chain Extender or the Chain Brancher is added to the rPET. 17. The method according to any one of claims 1 to 16, characterized in that the extruded melt is filtered before granulation. 18. The method according to any one of claims 1 to 17, characterized in that the extruded melt is pressed through a hole filter with a hole size between 30 µm and 300 µm and preferably between approximately 50 µm and 100 µm. 19. The method according to any one of claims 1 to 18, characterized in that an acid scavenger is added to the PET material prior to extrusion. 20. The method according to claim 19, characterized in that the acid scavenger used is calcium stearate, zinc stearate, zinc oxide or hydrotalcite or a combination of the aforementioned acid scavengers. 21. The method according to any one of claims 1 to 20, characterized in that the material is degassed during extrusion. 22. The method according to any one of claims 1 to 21, characterized in that the rPET material obtained in method step f) is fed to the EBM system and a chain extender or chain branch is again metered into the EBM system. 23. The method according to any one of claims 1 to 22, characterized in that the melt is divided into thin layers or strands in the extruder. 24. The method according to any one of claims 1 to 23, characterized in that the extrusion takes place in a vacuum or in a protective gas atmosphere, in particular under nitrogen. 25. The method according to any one of claims 1 to 24, characterized in that a tube is extruded, blown into a hollow body and then cut off. 26. The method according to any one of claims 1 to 25, characterized in that the strength of the hose is increased by active cooling by 5 to 50 ° C. 27. The method according to claim 27, characterized in that the hose is cooled by expansion of the hose, contact with another medium, blow nozzles, aerosols or other forms of heat dissipation, in particular by means of heat pipes. 28. The method according to any one of claims 1 to 27, characterized in that "untreated" PET (new goods or rPET) with an IV of 0.6 to 0.95 dl / g in a mass fraction of 0 to 50% is added to the PET, to adjust the melt strength for each item. 29. Hollow bodies, in particular bottles, made of at least partially recycled PET, characterized, that the PET starting material for the production of the hollow body is between 30 percent by weight. and 100 percent by weight rPET with an intrinsic viscosity between 0.90 and 1.5 dl / g and an extensional viscosity of more than 5500 Pa * s, preferably more than 6500 Pa * s, and particularly preferably more than 7000 Pa * s, and between 70 wt. Contains% and zero% by weight of vPET. 30. Hollow body according to claim 29 obtainable by the method according to one of claims 1 to 29. 31. Hollow body according to claim 29 or 30, characterized in that the recycled PET is made from recycled post-consumer PET with a viscosity between 0.65 and 0.84 dl / g by condensation. 32. Hollow body according to one of claims 29 to 31, characterized in that the PET starting material for producing the hollow body has a shear viscosity at 275 ° C and 50s <-1> of less than 3000 Pa * s, in particular between 1000 and 2500 Pa * s has. 33. Hollow body according to one of claims 29 to 32, characterized in that the PET starting material for producing the hollow body has an extensional viscosity of at least 5500 Pa * s at 275 ° C (50s <-1>) in the production of small hollow bodies and more than 6500 Pa * s and in particular between 7000 Pa * s and 14000 Pa * s for hollow bodies with a volume of more than 500 ml and preferably more than 600 ml.